New illnesses don't always burst upon the world in dramatic fashion, as sudden acute respiratory syndrome did several years ago. Sometimes, as was the case with progressive inflammatory neuropathy, they first appear as unobtrusively as exhausted factory workers dragging themselves up a long flight of stairs.
Carole Bower, MSN, RN, manager of occupational health at Quality Pork Processors, a large slaughterhouse in Austin, Minnesota, was treating two workers who had been on disability because of neurologic symptoms. She noticed that they had difficulty climbing the stairs to the third floor clinic. Over several months in late 2006 and early 2007, several other employees reported a similar and unusual combination of symptoms: overwhelming muscle fatigue and weakness, numbness, and tingling in the legs. Some also reported weakness and sensations in their arms. Bower and her two colleagues, Jan Johnson, RN, and Diana Barrera, LPN, began to suspect that they were dealing with an occupational illness that had something to do with the slaughterhouse environment.
Bower notified the plant's management and referred the workers to nearby Austin Medical Center, part of the Mayo Health System. They were subsequently evaluated by peripheral neuropathy specialists at the Mayo Clinic in Rochester, Minnesota, who in turn notified the Minnesota Department of Health. "We just felt so concerned about these employees," Bower told AJN. "We felt that openness to the investigation was the best response for the corporation. We provided open access to the plant, the equipment, and the employees-those who had symptoms and those who didn't."
Stacy Holzbauer, DVM, MPH, DACVPM, a public health officer at the Centers for Disease Control and Prevention (CDC) who had been assigned to the Minnesota Department of Health as part of a two-year training program, participated in the epidemiologic investigation. "Carole was very astute in recognizing that something was going on, and we were fortunate that the patients were all sent to the same medical facility," she said. "The continuity of care made it a lot easier for people who were experts in the field to agree that something was wrong and that it was a new syndrome." She added that "the plant was completely cooperative from day one."
The illness is called progressive inflammatory neuropathy (PIN), according to the CDC. (For a "working case definition" of PIN and a discussion of this investigation, go to http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5705a3.htm). Although it's similar to both acute and chronic inflammatory demyelinating polyneuropathies, "its neurological symptoms have an unusual pattern of progression," said Aaron DeVries, MD, MPH, a medical epidemiologist in the infectious disease prevention and control section of the Minnesota Department of Health. "Other similar illnesses progress either very rapidly or very slowly. This one falls somewhere in the middle."
According to DeVries, Guillain-Barre syndrome, for example, an acute inflammatory demyelinating neuropathy, typically progresses over the course of a few days to a few weeks and resolves fairly quickly; in contrast, chronic inflammatory demyelinating polyradiculoneuropathy may progress over several months to several years, and resolves very slowly, if at all.
Investigators found nothing unique about the pigs that were processed in the plant and nothing to indicate a food-borne pathogen, so they knew the meat the plant produced posed no danger to consumers. They conducted extensive interviews with affected workers, checking medications, vaccinations, travel history, and possible exposures to chemicals and other toxins. They found no factor common to all of them except that those who were affected worked in a particular part of the slaughterhouse.
Think of a slaughterhouse as an assembly line in reverse, where whole animals are disassembled piece by piece. The pig enters at one end of the facility and is killed, bled, and skinned. Next the internal organs, head, and feet are removed and the carcass is split in half in the "warm room." Then in the "cold room" the carcass halves are further divided into the cuts of meat that are sold to wholesalers. At Quality Pork Processors, roughly 17,000 pigs are processed each day.
The investigators discovered that all of the affected employees worked in the warm room, and all were stationed at or had regular contact with the "head table." Here, about 40 workers per shift harvest the skeletal muscle that surrounds the skulls-a prime ingredient in pork sausage-and, as a last step, blow the brains out of the skulls with a high-pressure compressed air system, exposing those in the area to spattered and perhaps aerosolized neurologic tissue. In all, there have been 16 confirmed cases of PIN and one probable case since 2004, Holzbauer said. The practice of blowing brains out of pig skulls was stopped and active surveillance is ongoing.
Once the common work area was discovered, the CDC worked with the U.S. Department of Agriculture and several other federal and state agencies to survey similar plants, focusing on the 25 largest swine slaughterhouses in the country. Only two other plants, in Indiana and Nebraska, were using the compressed air devices to blow out the pig brains. Eight additional cases of PIN were eventually found (six confirmed and one probable case in Indiana and one confirmed case in Nebraska), bringing the total to two probable and 23 confirmed cases. Again, proximity to the head table-the brain removal operation-seemed to be the common factor.
The cause of the illness is still under investigation. So far, no infectious agents have been found. One likely hypothesis is that the illness is an autoimmune disorder: either by inhalation or mucus membrane contact, a person is exposed to some component of the pig's neurologic tissue (perhaps a protein or a lipid), and the immune system develops antibodies that then attack the body's own nerve tissue as if it were foreign matter. Those who develop this response may or may not be genetically predisposed to it.
According to Holzbauer and DeVries, only a few patients have had prolonged symptoms; most have recovered either on their own or with treatment, usually with steroids, plasma exchange, or IV immunoglobulin therapy, as well as physical therapy. But no one really knows whether these treatments are effective because the case numbers are so small.
Three of the workers remain on disability, but the rest are working full time, although some still aren't ready for heavy lifting. "Many of our employees are immigrants," Bower noted, "so we help with their need for interpreters, as well as managing their medical appointments and transportation." She said the plant's management has been very accommodating to the workers' need for flexible schedules and reassignment to less-demanding tasks. As for the impact of the investigation and the discovery of the new syndrome, Bower said, "This has been significant for all of us." She noted with satisfaction that once the plant discontinued the practice of removing brains with compressed air, there have been no new cases of PIN.
James M. Stubenrauch, senior editor